Low blood oxygen, known as hypoxemia, means that the level of oxygen in the blood has fallen below normal levels, due to one or more of many different causes. Under most circumstances, breathing room air, normal readings range from 95 to 100 percent. Levels under 90 percent are considered low, so you probably are worrying unnecessarily.
Oxygen levels are best measured via an arterial blood gas test that also measures carbon dioxide and pH or, less precisely, with an oximeter, a device that clips on the end of a finger and shines a light through it. The color of the light coming out the other side is analyzed by a tiny computer in the device to determine your blood oxygen level.
Among the long list of conditions that can cause hypoxemia are anemia, heart defects present at birth (congenital heart disease), COPD and emphysema, high altitude, pneumonia, shock, and sleep apnea. Symptoms of low blood oxygen are shortness of breath after slight exertion or at rest and feeling tired after little effort.
Another cause of low blood oxygen is a condition called obesity hyperventilation syndrome (OHS) in which poor breathing leads to too much carbon dioxide and too little oxygen. While the exact cause of this condition isn't known, it is believed to stem from two factors:
- A defect in the brain's control over breathing
- Excessive fatty-tissue weight against the chest wall.
Most of those affected also have sleep apnea; many of the symptoms of OHS are likely due to lack of sleep - daytime sleepiness, depression and headaches. Weight loss can help reverse this condition, but short of that, the only treatments are a ventilation mask used mainly during sleep and supplemental oxygen delivered via a tube through the neck.
If you have chronic shortness of breath due to low oxygen, quit cigarettes if you smoke and avoid secondhand smoke, which can only make matters worse. Also try to get regular exercise, a tough but vital prescription.
Andrew Weil, M.D.